The trims of automobiles are usually subjected to facing processing, for example, by applying a prescribed size of a cloth (e.g. moquette fabrics, tricot fabrics, etc.) to the surface thereof, applying a skin covering to whole surface including the region applied with a cloth by vacuum forming, treating the periphery of the overlapped region of the cloth and the skin covering by high frequency welding, and then removing a part (surplus) of the skin covering to expose the cloth. As the skin covering, there is usually used a polyvinyl chloride sheet, which is melt-adhered with the cloth by high frequency welding, but this skin covering has insufficient strength and adhesion. In order to improve the adhesion, it has been proposed to use a low polymerization polyvinyl chloride. The low polymerization polyvinyl chloride is effective for improving the melt adhesion, but it results in defect (breaking of the covering, etc.) in the vacuum forming processing.